1. Field of the Invention
This invention relates to fragmentation warheads.
2. Description of the Related Art
Fragmentation warheads expel metal fragments upon detonation of an explosive. Fragmentation warheads are used as offensive weapons or as countermeasures to anti-personnel or anti-property weapons such as rocket-propelled grenades. A typical warhead includes an explosive inside a steel case. A booster explosive and safe and arm device are positioned in an aft section of the case to detonate the explosive. A fragmentation assembly is placed in an opening in a fore section of the case against the flat leading surface of the explosive. The fragmentation assembly will typically include ‘scored’ metal or individual fragments such as spheres or cubes to control the size and shape of the fragments so that the fragments are expelled in a predictable pattern and speed. Scored metal produces about an 80% mass efficiency while individual fragments are expelled with mass efficiency approaching 100% where mass efficiency is defined as the ratio of fragment mass expelled (therefore effective against the intended target) to the total fragment mass. In other words, the mass efficiency is the ratio of the total mass less the interstitial mass that was consumed during the launch process (therefore ineffective against the intended target) to the total mass.
The steel case confines a portion of the radial energy of the pressure wave (albeit for a very short duration) caused by detonation of the explosive and redirects it along the body axis of the warhead to increase the force of the blast that propels the metal fragments forward with a lethality radius of, for example, 25-50 meters. The lethality radius is defined as the radius of a virtual circle composed of the sum of all lethal areas (zones) meeting a minimum lethal threshold. For example, the lethality threshold may occur when 1% of people at that radius are killed. These fragments are generally expelled in a forward cone towards the intended target. The density of fragments per unit area is maximum near zero degrees and falls off with increasing angle with tails that extend well beyond the desired cone. As a result, the warhead has a maximum lethality confined to a very narrow angle and expels a certain amount of lethal fragments outside the desired target area that may cause collateral damage. As a result, the aimpoint and detonation timing tolerances to engage and destroy the threat while minimizing collateral damage are tight.
Detonation of the high explosive produces a gas blast that has a much smaller lethality radius, maybe 3 meters in this example, in all directions caused by the pressure wave of the blast. The detonation also tears the steel case into metal fragments of various shapes and sizes that are thrown in all directions, beyond the lethality radius of the gas blast. In this example, the expelled metal fragments from the case may have a lethality radius of 5-8 meters. Detonation of the steel case increases the potential for collateral damage without improving the lethality of the warhead to destroy the threat.